It is known from the prior art that some microtechnical parts made of single crystal or polycrystalline materials, such as resonators, are made by etching. This technique consists in taking the substrate to be etched and depositing a layer of photosensitive resin on top. A mask is placed on the resin and the whole assembly is exposed to light so that the photosensitive resin structure exposed to light is modified. This modified resin is eliminated by the action of a chemical element thus stripping the substrate bare at the places where the resin has been eliminated.
Subsequently, these bare regions of the substrate are chemically etched in order to create hollow portions. The chemical agent is chosen to etch only the material forming the substrate and not the unmodified photosensitive resin. The duration of this chemical etching step determines the dimensions of the hollow portions.
Similarly, it is possible to envisage making microtechnical parts by machining and/or polishing so that a drill or polisher may be used to form said parts.
A first drawback of this chemical etching technique is that it cannot produce hollow portions with straight sides or walls. Indeed, the hollow portions obtained have inclined sides. This means that the surface of the hollow portion varies with depth, i.e. the surface becomes larger or smaller with the depth of the hollow. Generally the surface becomes smaller with depth. This observation means that theoretical calculations have to be adapted to obtain hollow portions with straight sides. Further, this variation in the profile of the hollow portions between theory and practice results in a variation in characteristics.